When \(b=0\) , see Fig. REF (a), momentum spectrum is same as in Fig. 6(a) of Ref. [1]}. At large spatial scale \(\lambda =500m^{-1}\) , when \(b=0\)  , a very weak oscillation can be observed. For small chirp, we can see stronger oscillation on the two sides of momentum spectrum in Fig. REF (b). For the large chirp, very strong oscillation appears, meanwhile, momentum spectrum shrinks and shifts to positive direction, see Fig. REF (c) and (d). These oscillations can be understood as interference effect of particles created by opposite signed large peaks of the temporal field [2]}.
